Client access license

A client access license (CAL) is a commercial software license that allows client computers to use server software services. Most commercial desktop apps are licensed so that payment is required for each installation, but some server products can be licensed so that payment is required for each device or user that accesses the service provided by the software. For example, an instance of Windows Server 2016 for which ten User CALs are purchased allows 10 distinct users to access the server.